The objective of this proposal is to maintain and enhance the specific pathogen-free (SPF) rhesus macaque supply and breeding colony program at the Caribbean Primate Research Center (CPRC). This program consists of two SPF colonies (one closed and the other open). While the closed colony growths only by births, the open colony increases its size not only by births, but also by incorporating SPF candidates to its cohort. The closed colony (referred as to the U24 SPF colony) will consist of a minimum of 652 animals, and the open colony (referred as to SPF-A) will start with 468 animals. Thus, the founding stock of these genetically-characterized Indian-origin monkey colonies will be donated by CPRC and will consist of approximately 1,120 SPF (Herpes B, STLV-1, SIV and SRV-free) rhesus macaques. About 82 (7%) of the U24 SPF animals will be also free of the papovavirus SV40. Thus, this program will consist of two U24 SPF sub colonies: one SV40-free and the other SV40 positive. Animals from these SPF sub colonies will be maintained in well-defined and separated areas, will be housed in reproduction corncribs, and will be quarterly tested for the presence of the above mentioned target viruses. All SPF colonies will be closely monitored by well-established genetic and virology techniques and assays. A panel of highly polymorphic genetic markers will be used to characterize the U24 SPF and SPF-A colonies and to optimize the structure of breeding groups, maximizing the level of their genetic heterogeneity. At the end of this four year grant, the SPF-A colony will be closed. The entire program will produce a total estimated offspring of more than 1,350 SPF rhesus macaques, of which 96 will be also SV40 negative. It is expected that the SPF colonies of this program will make available to PHS-funded grants about 300 animals/year and that it will attain self-sufficiency by the end of this grant. CPRC SPF macaques will help meet the increased research demand that exists for these animals. Our Center will continue to make significant contributions to AIDS and to other research programs by providing high quality, healthy, and genetically-characterized SPF rhesus monkeys to NIH-sponsored research initiatives.